The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.
Four p38 MAPK isoforms (alpha, beta, gamma and delta respectively), each displaying different patterns of tissue expression, have been identified. The p38 MAPK alpha and beta isoforms are found ubiquitously in the body, being present in many different cell types. The alpha isoform is well characterized in terms of its role in inflammation. Although studies using a chemical genetic approach in mice indicate that the p38 MAPK beta isoform does not play a role in inflammation (O'Keefe, S. J. et al., J Biol Chem., 2007, 282(48):34663-71), it may be involved in pain mechanisms through the regulation of COX2 expression (Fitzsimmons, B. L. et al., Neuroreport, 2010, 21(4):313-7). These isoforms are inhibited by a number of previously described small molecular weight compounds. Early classes of inhibitors were highly toxic due to the broad tissue distribution of these isoforms which resulted in multiple off-target effects of the compounds. Furthermore, development of a substantial number of inhibitors has been discontinued due to unacceptable safety profiles in clinical studies (Pettus, L. H. and Wurz, R. P., Curr. Top. Med. Chem., 2008, 8(16):1452-67). As these adverse effects vary with chemotype, and each of these compounds has distinct kinase selectivity patterns, the toxicities observed may be structure—rather than p38 mechanism-based.
Less is known about the p38 MAPK gamma and delta isoforms, which, unlike the alpha and beta isozymes are expressed in specific tissues and cells. The p38 MAPK-delta isoform is expressed more highly in the pancreas, testes, lung, small intestine and the kidney. It is also abundant in macrophages and detectable in neutrophils, CD4+ T cells and in endothelial cells (Shmueli, O. et al., Comptes Rendus Biologies, 2003, 326(10-11):1067-1072; Smith, S. J. Br. J. Pharmacol., 2006, 149:393-404; Hale, K. K., J. Immunol., 1999, 162(7):4246-52; Wang, X. S. et al., J. Biol. Chem., 1997, 272(38):23668-23674.) Very little is known about the distribution of p38 MAPK gamma although it is expressed more highly in brain, skeletal muscle and heart, as well as in lymphocytes and macrophages. (Shmueli, O. et al., Comptes Rendus Biologies, 2003, 326(10-11):1067-1072, (2003); Hale, K. K., J. Immunol., 1999, 162(7):4246-52: Court, N. W. et al., J. Mol. Cell. Cardiol., 2002, 34(4):413-26; Mertens, S. et al., FEBS Lett., 1996, 383(3):273-6.)
Selective small molecule inhibitors of p38 MAPK gamma and p38 MAPK delta are not currently available, although one previously disclosed compound, BIRB 796, is known to possess pan-isoform inhibitory activity. The inhibition of p38 MAPK gamma and delta isoforms is observed at higher concentrations of the compound than those required to inhibit p38 MAPK alpha and p38 beta (Kuma, Y. J. Biol. Chem., 2005, 280:19472-19479). In addition BIRB 796 also impaired the phosphorylation of p38 MAPKs or JNKs by the upstream kinase MKK6 or MKK4. Kuma discussed the possibility that the conformational change caused by the binding of the inhibitor to the MAPK protein may affect the structure of both its phosphorylation site and the docking site for the upstream activator, thereby impairing the phosphorylation of p38 MAPKs or JNKs.
p38 MAP kinase is believed to play a pivotal role in many of the signalling pathways that are involved in initiating and maintaining chronic, persistent inflammation in human disease, for example, in severe asthma, COPD (Chung, F., Chest, 2011, 139(6):1470-1479) and inflammatory bowel disease (IBD). There is now an abundant literature which demonstrates that p38 MAP kinase is activated by a range of pro-inflammatory cytokines and that its activation results in the recruitment and release of additional pro-inflammatory cytokines. Indeed, data from some clinical studies demonstrate beneficial changes in disease activity in patients during treatment with p38 MAP kinase inhibitors. For instance Smith describes the inhibitory effect of p38 MAP kinase inhibitors on TNFα (but not IL-8) release from human PBMCs.
The use of inhibitors of p38 MAP kinase in the treatment of COPD and IBD has also been proposed. Small molecule inhibitors targeted to p38 MAPK α/β have proved to be effective in reducing various parameters of inflammation in:                cells and tissues obtained from patients with COPD, who are generally corticosteroid insensitive, (Smith, S. J., Br. J. Pharmacol., 2006, 149:393-404);        biopsies from IBD patients (Docena, G. et al., J. of Trans. Immunol., 2010, 162:108-115); and        in vivo animal models (Underwood, D. C. et al., Am. J. Physiol., 2000, 279:L895-902; Nath, P. et al., Eur. J. Pharmacol., 2006, 544:160-167.).        
Irusen and colleagues also suggested the possibility of involvement of p38 MAPKα/β on corticosteroid insensitivity via the reduction of binding affinity of the glucocorticoid receptor (GR) in nuclei (Irusen, E. et al., J. Allergy Clin. Immunol., 2002, 109:649-657). Clinical experience with a range of p38 MAP kinase inhibitors, including AMG548, BIRB 796, VX702, SCIO469 and SCIO323 has been described (Lee, M. R. and Dominguez, C., Current Med. Chem., 2005, 12:2979-2994.). However, the major obstacle hindering the utility of p38 MAP kinase inhibitors in the treatment of human chronic inflammatory diseases has been the toxicity observed in patients. This has been sufficiently severe to result in the withdrawal from clinical development of many of the compounds progressed, including all those specifically mentioned above.
COPD is a condition in which the underlying inflammation is reported to be substantially resistant to the anti-inflammatory effects of inhaled corticosteroids. Consequently, a superior strategy for treating COPD would be to develop an intervention which has both inherent anti-inflammatory effects and the ability to increase the sensitivity of the lung tissues of COPD patients to inhaled corticosteroids. A recent publication of Mercado (Mercado, N., et al., Mol. Pharmacol., 2011, 80(6):1128-1135) demonstrates that silencing p38 MAPK gamma has the potential to restore sensitivity to corticosteroids. Consequently there may be a dual benefit for patients in the use of a p38 MAP kinase inhibitor for the treatment of COPD and severe asthma.
Many patients diagnosed with asthma or with COPD continue to suffer from uncontrolled symptoms and from exacerbations of their medical condition that can result in hospitalisation. This occurs despite the use of the most advanced, currently available treatment regimens, comprising of combination products of an inhaled corticosteroid and a long acting β-agonist. Data accumulated over the last decade indicates that a failure to manage effectively the underlying inflammatory component of the disease in the lung is the most likely reason that exacerbations occur. Given the established efficacy of corticosteroids as anti-inflammatory agents and, in particular, of inhaled corticosteroids in the treatment of asthma, these findings have provoked intense investigation. Resulting studies have identified that some environmental insults invoke corticosteroid-insensitive inflammatory changes in patients' lungs. An example is the response arising from virally-mediated upper respiratory tract infections (URTI), which have particular significance in increasing morbidity associated with asthma and COPD.
Epidemiologic investigations have revealed a strong association between viral infections of the upper respiratory tract and a substantial percentage of the exacerbations suffered by patients already diagnosed with chronic respiratory diseases. Some of the most compelling data in this regard derives from longitudinal studies of children suffering from asthma (Papadopoulos, N. G., Papi, A., Psarras, S. and Johnston, S. L., Paediatr. Respir. Rev., 2004, 5(3):255-260). A variety of additional studies support the conclusion that a viral infection can precipitate exacerbations and increase disease severity. For example, experimental clinical infections with rhinovirus have been reported to cause bronchial hyper-responsiveness to histamine in asthmatics which is unresponsive to treatment with corticosteroids (Grunberg, K., Sharon, R. F., et al., Am. J. Respir. Crit. Care Med., 2001, 164(10):1816-1822). Further evidence derives from the association observed between disease exacerbations in patients with cystic fibrosis and HRV infections (Wat, D., Gelder, C., et al., J. Cyst. Fibros., 2008, 7:320-328). Also consistent with this body of data is the finding that respiratory viral infections, including rhinovirus, represent an independent risk factor that correlates negatively with the 12 month survival rate in paediatric, lung transplant recipients (Liu, M., Worley, S., et al., Transpl. Infect. Dis., 2009, 11(4):304-312).
Clinical research indicates that the viral load is proportionate to the observed symptoms and complications and, by implication, to the severity of inflammation. For example, following experimental rhinovirus infection, lower respiratory tract symptoms and bronchial hyper-responsiveness correlated significantly with virus load (Message, S. D., Laza-Stanca, V., et al., PNAS, 2008; 105(36):13562-13567). Similarly, in the absence of other viral agents, rhinovirus infections were commonly associated with lower respiratory tract infections and wheezing, when the viral load was high in immunocompetent paediatric patients (Gerna, G., Piralla, A., et al., J. Med. Virol., 2009, 81(8):1498-1507).
Interestingly, it has been reported recently that prior exposure to rhinovirus reduced the cytokine responses evoked by bacterial products in human alveolar macrophages (Oliver, B. G., Lim, S., et al., Thorax, 2008, 63:519-525). Additionally, infection of nasal epithelial cells with rhinovirus has been documented to promote the adhesion of bacteria, including S. aureus and H. influenzae (Wang, J. H., Kwon, H. J. and Yong, J. J., The Laryngoscope, 2009, 119(7):1406-1411). Such cellular effects may contribute to the increased probability of patients suffering a lower respiratory tract infection following an infection in the upper respiratory tract. Accordingly, it is therapeutically relevant to focus on the ability of novel interventions to decrease viral load in a variety of in vitro systems, as a surrogate predictor of their benefit in a clinical setting.
High risk groups, for whom a rhinovirus infection in the upper respiratory tract can lead to severe secondary complications, are not limited to patients with chronic respiratory disease. They include, for example, the immune compromised who are prone to lower respiratory tract infection, as well as patients undergoing chemotherapy, who face acute, life-threatening fever. It has also been suggested that other chronic diseases, such as diabetes, are associated with a compromised immuno-defence response. This increases both the likelihood of acquiring a respiratory tract infection and of being hospitalised as a result (Peleg, A. Y., Weerarathna, T., et al., Diabetes Metab. Res. Rev., 2007, 23(1):3-13; Kornum, J. B., Reimar, W., et al., Diabetes Care, 2008, 31(8):1541-1545).
Whilst upper respiratory tract viral infections are a cause of considerable morbidity and mortality in those patients with underlying disease or other risk factors; they also represent a significant healthcare burden in the general population and are a major cause of missed days at school and lost time in the workplace (Rollinger, J. M. and Schmidtke, M., Med. Res. Rev., 2010, Doi 10.1002/med.20176). These considerations make it clear that novel medicines, that possess improved efficacy over current therapies, are urgently required to prevent and treat rhinovirus-mediated upper respiratory tract infections. In general the strategies adopted for the discovery of improved antiviral agents have targeted various proteins produced by the virus, as the point of therapeutic intervention. However, the wide range of rhinovirus serotypes makes this a particularly challenging approach to pursue and may explain why, at the present time, a medicine for the prophylaxis and treatment of rhinovirus infections has yet to be approved by any regulatory agency.
Viral entry into the host cell is associated with the activation of a number of intracellular signalling pathways controlled by the relative activation and inactivation of specific kinases which are believed to play a prominent role in the initiation of inflammatory processes (reviewed by Ludwig, S, 2007; Signal Transduction, 7:81-88) and of viral propagation and subsequent release.
It has been disclosed previously that compounds that inhibit the activity of both c-Src and Syk kinases are effective agents against rhinovirus replication (Charron, C. E. et al., WO 2011/158042) and that compounds that inhibit p59-HCK are effective against influenza virus replication (Charron, C. E. et al., WO 2011/070369). For the reasons summarised above, in combination with the inhibition of p38 MAPKs, these are particularly advantageous inherent properties for compounds designed to treat chronic respiratory diseases.
Certain p38 MAPK inhibitors have also been described as inhibitors of the replication of respiratory syncytial virus (Cass, L. et al., WO 2011/158039).
The precise etiology of IBD is uncertain, but is believed to be governed by genetic and environmental factors that interact to promote an excessive and poorly controlled mucosal inflammatory response directed against components of the luminal microflora. This response is mediated through infiltration of inflammatory neutrophils, dendritic cells and T-cells from the periphery. Due to the ubiquitous expression of p38 in inflammatory cells it has become an obvious target for investigation in IBD models. Studies investigating the efficacy of p38 inhibitors in animal models of IBD and human biopsies from IBD patients indicated that p38 could be a target for the treatment of IBD (Hove, T. ten et al., Gut, 2002, 50:507-512, Docena, G. et al., J. of Trans. Immunol., 2010, 162:108-115). However, these findings are not completely consistent with other groups reporting no effect with p38 inhibitors (Malamut G. et al., Dig. Dis. Sci, 2006, 51:1443-1453). A clinical study in Crohn's patients using the p38 alpha inhibitor BIRB796 demonstrated potential clinical benefit with an improvement in C-reactive protein levels. However this improvement was transient, returning to baseline by week 8 (Schreiber, S. et al., Clin. Gastro. Hepatology, 2006, 4:325-334). A small clinical study investigating the efficacy of CNI-1493, a p38 and Jnk inhibitor, in patients with severe Crohn's disease showed significant improvement in clinical score over 8 weeks (Hommes, D. et al. Gastroenterology. 2002 122:7-14).
T cells are known to play key role in mediating inflammation of the gastrointestinal tract. Pioneering work by Powrie and colleagues demonstrated that transfer of naive CD4+ cells into severely compromised immunodeficient (SCID) animals results in the development of colitis which is dependent on the presence of commensal bacteria (Powrie F. et al. Int Immunol. 1993 5:1461-71). Furthermore, investigation of mucosal membranes from IBD patients showed an upregulation of CD4+ cells which were either Th1 (IFNγ/IL-2) or Th2 (IL5/TGFβ) biased depending on whether the patient had Crohn's disease or ulcerative colitis (Fuss I J. et al. J Immunol. 1996 157:1261-70.). Similarly, T cells are known to play a key role in inflammatory disorders of the eye with several studies reporting increased levels of T cell associated cytokines (IL-17 and IL-23) in sera of Behçets patients (Chi W. et al. Invest Ophthalmol Vis Sci. 2008 49:3058-64). In support, Direskeneli and colleagues demonstrated that Behçets patients have increased Th17 cells and decreased Treg cells in their peripheral blood (Direskeneli H. et al. J Allergy Clin Immunol. 2011 128:665-6).
One approach to inhibit T cell activation is to target kinases which are involved in activation of the T cell receptor signalling complex. Syk and Src family kinases are known to play a key role in this pathway, where Src family kinases, Fyn and Lck, are the first signalling molecules to be activated downstream of the T cell receptor (Barber E K. et al. PNAS 1989 86:3277-81). They initiate the tyrosine phosphorylation of the T cell receptor leading to the recruitment of the Syk family kinase, ZAP-70. Animal studies have shown that ZAP-70 knockout results in a SCID phenotype (Chan A C. et al. Science. 1994 10; 264(5165):1599-601).
A clinical trial in rheumatoid arthritis patients with the Syk inhibitor Fostamatinib demonstrated the potential of Syk as an anti-inflammatory target with patients showing improved clinical outcome and reduced serum levels of IL-6 and MMP-3 (Weinblatt M E. et al. Arthritis Rheum. 2008 58:3309-18). Syk kinase is widely expressed in cells of the hematopoietic system, most notably in B cells and mature T cells. Through interaction with immunoreceptor tyrosine-based activation (ITAM) motifs it plays an important role in regulating T cell and B cell expansion as well as mediating immune-receptor signalling in inflammatory cells. Syk activation leads to IL-6 and MMP release—inflammatory mediators commonly found upregulated in inflammatory disorders including IBD and rheumatoid arthritis (Wang Y D. et al World J Gastroenterol 2007; 13: 5926-5932, Litinsky I et al. Cytokine. 2006 January 33:106-10).
In addition to playing key roles in cell signalling events which control the activity of pro-inflammatory pathways, kinase enzymes are now also recognised to regulate the activity of a range of cellular functions. Among those which have been discussed recently are the maintenance of DNA integrity (Shilo, Y. Nature Reviews Cancer, 2003, 3:155-168) and co-ordination of the complex processes of cell division. An illustration of recent findings is a publication describing the impact of a set of inhibitors acting upon the so-called “Olaharsky kinases” on the frequency of micronucleus formation in vitro (Olaharsky, A. J. et al., PLoS Comput. Biol., 2009, 5(7):e1000446.). Micronucleus formation is implicated in, or associated with, disruption of mitotic processes and is therefore an undesirable manifestation of potential toxicity. Inhibition of glycogen synthase kinase 3α (GSK3α) was found to be a particularly significant factor that increases the likelihood of a kinase inhibitor promoting micronucleus formation. Recently, inhibition of the kinase GSK3β with RNAi was also reported to promote micronucleus formation (Tighe, A. et al., BMC Cell Biology, 2007, 8:34).
It may be possible to attenuate the adverse effects arising from drug interactions with Olaharsky kinases, such as GSK3α, by optimisation of the dose and/or by changing the route of administration. However, it would be more advantageous to identify therapeutically useful molecules that demonstrate low or undetectable activity against these off-target enzymes and consequently elicit little or no disruption of mitotic processes, as measured in mitosis assays.
It is evident from consideration of the literature cited hereinabove that there remains a need to identify and develop new p38 MAP kinase inhibitors that have improved therapeutic potential over currently available treatments. Desirable compounds are those that exhibit a superior therapeutic index by exerting, at the least, an equally efficacious effect as previous agents but, in one or more respects, are less toxic at the relevant therapeutic dose. The present invention therefore, inter alia, provides such novel compounds that inhibit the enzyme activity of p38 MAP kinase, for example with certain sub-type specificities, optionally together with Syk kinase and tyrosine kinases within the Src family (particularly c-Src) thereby possessing good anti-inflammatory properties, and suitable for use in therapy.
In one or more embodiments the compounds exhibit a long duration of action and/or persistence of action in comparison to other previously disclosed allosteric p38 MAP kinase inhibitors such as, for example, BIRB796 (Pargellis, C. et al., Nature Struct. Biol., 2002, 9(4):268-272).